The paper presents the results of calculations for determining neutron-physical characteristics (NFC) of fuelcontaining materials (FCM), including the possibility of formation of critical masses. The lack of reliable information at present about the material composition of some places of FCM requires additional studies to substantiate the nuclear safety of such clusters of FCM. An important and, in some cases, the only, method of investigating nuclear safety of places of FCM accumulation is the calculation method for determining the criticality parameters of FCM and predicting the change of neutron-physical characteristics important for nuclear safety during the planned time of FCM location in the «Ukryttya» object. Ensuring a reliable control of the intensity of fissions in FCM, as well as clarifying the supplementary cementitious material composition, requires the introduction of additional methods and channels for monitoring FCM, for example, on the activity of air and water environments determined by short-lived products of fission of nuclear fuel in FCM. The paper presents information on the predicted change in the neutron-physical characteristics of FCM for 120 years from the time of formation of FCM. In particular, the following characteristics are considered: neutron activity; alpha-activity; power of residual energy releases; change in the ratio of main alpha and neutron emitters; the effect of changes in other characteristics of FCM on subcriticality, as well as the conditions and configuration of possible criticality in FCM. For a long period of "planned" storage of FCM in the «Ukryttya» object facility, some NFC FCM will undergo significant changes. The main decline in residual energy releases, and, accordingly, FCM activity, including neutron activity, occurred in the first years after the accident. After more than 30 years, the rate of change of these characteristics of FCM significantly decreased.
Keywords: neutron-physical characteristics, fuel-containing materials, criticality parameters, nuclear safety, «Ukryttya» object.
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